A compact reducer with a large reduction ratio is necessary as a structure that turns a nacelle for a wind-power-generation wind turbine. For example, Patent Document 1 discloses a wind turbine driving apparatus which includes a first-stage reduction part and the second-stage reduction part, each of which comprises an epicyclic gear mechanism, coupled in series.
The first-stage reduction part is an offset reducer that includes a first-stage internal gear as a pin-like member, a first-stage external gear, a first-stage crank shaft, and a first-stage carrier, etc. The second-stage reduction part is an offset reducer that includes a second-stage internal gear as a pin-like member, a second-stage external gear, a second-stage center cluster shaft, a second-stage guide crank shaft, and a second-stage carrier, etc. According to such a wind turbine driving mechanism, the driving force by a motor is input into the first-stage reduction part, is subjected to speed reduction, input into the second-stage reduction part, and is subjected to further speed reduction.
The wind turbine driving mechanism disclosed in Patent Document 1 has the first-stage reduction part and the second-stage reduction part disposed over the axial lines of the crank shaft and the carrier, and coupled in series in order to obtain a large reduction ratio. However, since this wind turbine driving mechanism employs a structure having the first-stage reduction part and the second-stage reduction part disposed and coupled in series, the dimension in the axial direction is large, and is disadvantageous for downsizing of the whole device.